Recently, due to the high integration level of semiconductor devices, semiconductor devices have been structured in multiple layers. Accordingly, a polishing process for planarizing layers of a semiconductor wafer is indispensably included in a fabrication process of the semiconductor devices. One known polishing process, CMP, is mainly being used.
The CMP process is a process for polishing a surface of a wafer coated with tungsten, oxide, etc., through the use of mechanical friction, as well as a chemical polishing agent. The mechanical portion of the CMP polishes a surface of a semiconductor wafer using friction between a polishing pad and the surface of the semiconductor wafer by rotating the wafer fixed on a rotating polishing head, with the wafer pressed against the polishing pad. The chemical portion of the CMP polishes the surface of the wafer using a slurry supplied between the polishing pad and the wafer as the chemical polishing agent.
This CMP process results in excellent planarity in a wide region as well as a narrow region. Accordingly, CMP is particularly adapted to the trend toward enlargement of wafer diameter.
Referring to FIG. 1, which illustrates a schematic configuration of a conventional CMP apparatus for performing the CMP process, the CMP apparatus generally includes a polishing station 110 and a polishing head assembly 120.
The polishing station 110 has a platen 114 on which a polishing pad 112 is placed. The polishing head assembly 120 includes a polishing head 122 for adsorbing a wafer W in a vacuum and an arm 124 connected to the polishing head 122. An actuator (not shown) loadings/unloadings the polishing head 122 on/from the polishing pad 112. The polishing station 110 may also utilize a vacuum supply unit (not shown), a compressed air supply unit (not shown), etc. In FIG. 1, reference numeral 126 denotes a slurry supply nozzle.
In the CMP process using the CMP apparatus as configured above, one conventional method for controlling uniformity of the wafer in order to secure a margin of depth of focus (DOF) in a photolithography process includes adjusting the number of turns of the platen and the polishing head. A pressure applied to the polishing head may also be adjusted in an attempt to achieve uniformity.
In addition, recently, there has been proposed a method for adjusting a pressure applied to the polishing head, such that different pressures are applied to different zones of the wafer for improving the uniformity of the wafer.
The above-mentioned conventional methods are disclosed in U.S. Pat. Nos. 6,056,631, 6,179,956, and 6,293,845.
However, when the wafer W is polished using the conventional CMP apparatus, a problem arises in that it is not easy to control the uniformity in the CMP process.